1. A bright, diffuse area of radio emission seen on one or both sides of the nucleus of a radio galaxy or other active galaxy and situated far outside the visible confines of the galaxy. The emission is mainly synchrotron radiation. The lobe is believed to consist of material ejected from the nucleus of the galaxy and transported into intergalactic space along a jet.

2. A region of high sensitivity appearing as a bulge in the antenna pattern of a radio telescope.